How do you understand the Bjarne's comments about exception specification? Especially, "not required to be checked across compilation-unit" and "violations will not be caught at run time"?

section 14.6.1 Checking Exception Specifications

--------------------
Importantly, exception-specifications are not required to be checked exactly across compilation-unit boundaries. Naturally, an implementation could check. However, for many large and long-lived systems, it is important that the implementation does not -- or, if it does, than it carefully gives hard errors only where violations will not be caught at run time.
--------------------

--------------------
However, for many large and long-lived systems, it is important that the implementation does not -- or, if it does, than it carefully gives hard errors only where violations will not be caught at run time.
--------------------

Quote:

Originally Posted by King Mir

It means that if exception specifications in two different compilation units disagree, that does not have to be a compile time error. It is however, undefined behavior.